Evaluation of 8 ergonomic computer mice

a regular mouse and

the HandShoeMouse by Hippus

Professor C.J. Snijders PhD, former head dept. of Biomedical Physics and Technology, Erasmus MC, University Medical Center Rotterdam

EMG measurements executed by IDEE University of Maastricht

© Erasmus MC 2007

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Types of physical load

extensor muscle load, hand & fingers hover above the mouse

Cinderella effect, exertion of unnecessary static forces

gripping and pinching

too large supination angle

excessive ulnar deviation of the wrist, “hand shake position”

excessive extension of the wrist

hand and lower arm hover above an object

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Physical load type I

With the existing computer mouse fingers have to remain elevated in between switching to prevent inadvertant switching.This results in extensor load.

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Fingers and hand hover above the mouse

Extensor load

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EMG data from fundamental research

visible moments of rest no moments of rest

EMG values show the level of muscle activity

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Physical load type II

Cinderella effect, exertion of unnecessary static forces:

extensor load, tonic muscles act continuously

special motor units (type I muscle fibres) control lesser forces,

are continuously active resulting in irritation and aggravation

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Physical load type III

Objects that induce gripping and pinching due to shape:

the regular mouse, too small for the average hand,

held between thumb, ring finger and little finger

thin, pen like objects, held between thumb, ring finger and

little finger

handle shape objects, gripped by the entire hand

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Physical load type IV

A too large supination angle: objects force hand and lower

arm in a strained position:

relaxed hand supination angle of around 150

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Physical load type V

“Hand shake position”, a too large supination angle combined

with an excessive ulnar deviation :

The hand is forced in a position resulting in an ulnar deviation of

the wrist outside the regular functional area.

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Physical load type VI

A too large extension angle of the wrist:

Corresponding with load type V the hand and wrist are forced

outside the functional area.

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Physical load type VII

Hover the hand and arm above an object:

For example the use of a pen in combination with a tablet forces

hand and possibly lower arm in a hovering position to allow for a

free motion over the tablet.

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Evaluation of ergonomic computer mice

A number of ergonomic computer mice were made available for

the evaluation programme. The use of these mice resulted in

complaints with the users. The source of these complaints could

in general be attributed to the aforementioned 7 types of

physical load factors.

Muscle exertion has been measured by means of EMG

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Evaluation of ergonomic computer mice

IDEE University Maastricht, the Netherlands, has performed the

necessary EMG measurements.

The protocol consisted of:

10 sec. rest,

10 sec. motion,

10 sec. rest

10 sec motion, however with the left button active.

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Evaluation of ergonomic computer mice

EMG-measurement set-up:

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EMG signal of extensor muscles

extensor carpi radialis longus

extensor carpi radialis brevis

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Evaluation of ergonomic computer mice

9 computer mice and the HandShoeMouse by Hippus were

measured by means of EMG while the various physical load

factors were analyzed.

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Source of physical load

excessive extensor load

excessive thumb load

instigates working from the wrist

instigates gripping and pinching

Regular mouseIn general the regular mouse is too small for the average hand resulting in a grip like action of thumb, ring finger and little fingerand thus excessive loads on metacarpal bones and ligaments.

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EMG signal of a regular mouse

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

a too large supination angle

hand rests on its side

mouse is gripped between palm of the hand, fingers and thumb

this position instigates gripping and pinching

metacarpal bones and ligaments are stressed

excessive tension in muscles of the lower arm

Vertical mouseForces the hand in an almost vertical position. The hand rests on its side. This generates excessive friction between hand and table top while working.

Ref. publication prof. Han Min Chen “The effect on forearm and shoulder muscle activity in using different slanted computer mice”

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EMG signal of vertical mouse

Evoluent

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

A-symmetrical ball mouseThe ball acts counter productive. The XY coordinates provided by the desk top are no longer used.

Operating the ball by means of the thumb carries an additional risk when the arterial flow is restricted. Synovia production can be inhibited resulting in calcitic deposits on the tendon.(referte Morbus de Quervain)

excessive extensor loads (fingers)

no arm movement, risk of restricted arterial flow

ball leads to excessive thumb load

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EMG signal of a-symmetrical ball mouse

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

excessive extensor loads (fingers)

no arm movement, risk of restricted arterial flow

ball inhibits the support of the hand, no rest possible

Symmetrical ball mouseThe ball acts counter productive. The XY coordinates provided by the desk top are no longer used.

Too little support is provided for the hand, this instigates switching with the thumb.

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1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

EMG signal of symmetrical ball mouse

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Source of physical load

Hand forced in a pre-set vertical positionThe weight of the hand rests on the side. The wrist is forced in an elevated position. This strained position results in awkward movements.

Ref. publication prof. Han Min Chen “The effect on forearm and shoulder muscle activity in using different slanted computer mice”

a too large supination angle

an excessive ulnar deviation “hand shake” position

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EMG signal of fixed vertical mouse

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

Pen mouseA thin pen-like object, does not provide support for the hand. Extensor muscles are continuously active.

too thin

shape instigates gripping and pinching

no support provided

instigates motions from the wrist

no stability, no rest for the hand

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EMG signal pen mouse

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

too thin

shape instigates gripping and pinching

no support provided

instigates motions from the wrist

extensor muscles are continuously active

Pen and tabletThe pen is too thin and thus cumbersome, instigates gripping and pinching.

Hovering hand (and arm) above a tablet causes unnecessary stresses and strains in lower (extensor) and upper arm muscles

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EMG signal pen and tablet

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

Mouse with horizontal buttonsFingers hover in a horizontal position above the buttons and have to be continuously lifted to avoid inadvertant switching.The hand slides from the body due to lack of support.The application of a “scroll wheel” at the side while no support is provided, generates a risk for the thumb joint.(referte Morbus de Quervain)

excessive extensor load

scroll wheel at the side

no thumb rest

shape instigates gripping and pinching

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EMG signal of mouse with horizontal buttons

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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Source of physical load

a too large supination angle

hand is positioned on its side

one grips the handle

position instigates excessive gripping and pinching

Joystick, mouse with handleThis mouse instigates gripping and pinching. As a result muscles are excessively strained and arm movement is restricted.

Ref. publications in Clinical Biomechanics by prof. Han Min Chen “The effect on forearm and shoulder muscle activity in usingdifferent slanted computer mice” and Gustafsson and Hagberg “computer mouse use in two different hand positions: exposure, comfort, exertion and productivity”

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EMG signal joystick, mouse with handle

1. extensor carpi radialis longus (red line)

2. extensor carpi radialis brevis (yellow line)

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EMG signal joystick, mouse with handle

flexor carpi radialis (red line)

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Minimal physical loads with the HandShoeMouse

hand, wrist and thumb are fully supported

extensor muscles are relaxed

shape prevents gripping and pinching

scroll wheel positioned between index and middle finger

to stimulate arterial flow large movements are possible

The HandShoeMouseThe shape is based on the hand in a relaxed position.Fingers and thumb rest supported. A light contraction of flexor muscles suffices to switch. The scroll wheel is positioned close to the finger tips to allow for minimal movements.

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EMG signal of the HandShoeMouse

1. m. extensor carpi radialis longus (red line)

2. m. extensor carpi radialis brevis (yellow line)

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EMG signal of the HandShoeMouse

flexor carpi radialis (red line)

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Conclusion

mice investigated show on average high EMG values

EMG values of extensor muscles indicate high level of activity

a number of mice show continuous high flexor loads

with a number of mice hand and/or arm are forced into

positions which cause unnecessary stresses and strains

the design is based on the natural relaxed position of

hand and arm

shape and weight realize a reduction of muscle load and thus

EMG values

the HandShoeMouse supports the hand continuously, during

action as well as in rest

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